Method for influencing the level of a radio-frequency transmitted signal in a base station in a fixed radio network

ABSTRACT

A method for influencing the level of a radio-frequency transmitted signal in a base station in a fixed radio network wherein the level of the radio-frequency transmitted signal is measured, and the level difference from the measured levels is determined in a transmitting/receiving unit and in an antenna transmitting/receiving unit which is connected to the transmitting/receiving unit via a cable. The level of the transmitted signal is influenced in such a manner that the level difference which is determined is maintained approximately at a predetermined level difference so as to compensate for level fluctuations in the transmitted signal caused by different cables and environmental influences.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, generally, to a method for influencingthe level of a radio-frequency transmitted signal in a base station in afixed radio network and, more particularly, to such a method wherein thelevel of the transmitted signal is first measured in atransmitting/receiving unit and then measured in a subsequent antennatransmitting/receiving unit such that a level difference is determinedand the level is then influenced so as to approximately maintain apredetermined level difference.

2. Description of the Prior Art

In order to produce a fixed radio network, radio base stations areprovided to which network termination devices are connected withoutwires. A network termination device represents the termination of acommunications network (for example, a public or private communicationsnetwork). The network termination device provides an interface (forexample, an analog or digital telephone or ISDN interface) to whichcommunications terminals (for example, analog or digital telephoneterminals or ISDN communications terminals) are connected. Theinformation to be transmitted from or to the communications terminals istransmitted via radio signals, which are formed in accordance witheither the standardized DECT transmission method or the CDMAtransmission method, via the radio path between the network terminationdevices and the radio base stations.

In a radio base station, a radio-frequency signal which is to betransmitted is formed, for example, in accordance with the CDMAtransmission method. In order to avoid considerable attenuationresulting from transmission via a cable, in particular a coaxial cable,the transmitted signal is transmitted at a lower level or at a lowerpower via a cable to an antenna transmitting/receiving unit. The antennatransmitting/receiving unit contains a line amplifier and is connectedto an antenna which transmits the radio-frequency transmitted signal asa radio signal. The antenna transmitting/receiving unit is generallyfitted at the upper end of an antenna mast close to the antenna. A radiosignal is received in the network termination device, and theradio-frequency received signal which is received is used to derive thetransmitted information. The antenna transmitting/receiving unit alsocontains a low-noise amplifier for a received signal. The receivedsignal is passed directly from the antenna, if thetransmitting/receiving unit and the antenna transmitting/receiving unitare separate, or via a transmission/reception diplexer in the case of ajoint transmitting/receiving antenna, to the amplifier.

The power of the transmitted radio signal or the level of theradio-frequency transmitted signal is, in this case, influencedsignificantly not only by the level change caused, for example in thecase of CDMA transmission method, by the transmission method which isused, but also by the antenna transmitting/receiving unit and by the RFcable or line which leads to the radio base station. Depending on thenature and length of the cable which is used, the level of theradio-frequency transmitted signal may have widely differing levelvalues. Furthermore, in widely different temperature conditions, forexample direct solar radiation during the day and low nighttimetemperatures, the antenna transmitting/receiving unit will amplify theradio-frequency transmitted signal to considerably different extentsand, thus, will additionally influence the level of the radio signal.Furthermore, the level of the received signal at the radio base stationis influenced. Particularly in the case of the CDMA transmission method,precise control of the level of the radio-frequency transmitted signalrepresents a major function which is used to achieve optimum receptionconditions in the network termination devices and minimum interferencein the further network termination devices. Since level fluctuations inthe received radio signal, particularly in radio networks using the CDMAtransmission method, can lead to different reception power levels in thenetwork termination devices as will as to operation which is subject tointerference, the radio signal which is received there or theradio-frequency transmitted signal in the radio base station should beat a level which is predetermined as much as possible.

An object to which the present invention is directed, therefore torefine a radio base station and the transmission path in a radio basestation in such a manner that a radio signal is transmittedapproximately at the intended level by the antenna, withtransmission-method-dependent level changes having to be ensured.

SUMMARY OF THE INVENTION

The major aspect of the method of to the present invention ensures thatthe level of the transmitted signal which is passed to it is measured inthe transmitting/receiving unit, and the level of the transmitted signalwhich is transmitted via the cable is measured in the antennatransmitting/receiving unit. The level difference between the measuredlevels is then determined and compared with a predetermined leveldifference, and the level of the transmitted signal is influenced insuch a manner that the level difference which is determined ismaintained approximately at the predetermined level difference. In thisway, the overall gain of the arrangement formed by thetransmitting/receiving unit, the cable and the antennatransmitting/receiving unit is set to a predetermined value or gainfactor, and this setting is monitored and, if necessary, readjusted.

The comparison of the level differences and the influencing of thetransmitted signal can be carried out in the transmitting/receiving unitor, alternatively, in the antenna transmitting/receiving unit, with themeasured levels being transmitted to the transmitting/receiving unit orto the antenna transmitting/receiving unit. A major advantage of themethod of the present invention is that the level of transmitted signalat the antenna is kept approximately at a value which is dependent onthe transmission method, irrespective of the length and transmissioncharacteristics—particularly, attenuation) of the cable between thetransmitting/receiving unit, in which case the different transmissioncharacteristics are caused by different cable types and by environmentalinfluences such as severe temperature fluctuations. The transmittedsignal level control according to the present invention allows optimumreception conditions to be ensured in the network termination devices.

According to one advantageous embodiment of the method of the presentinvention, the level of the transmitted signal which is transmitted viathe cable is measured in the antenna transmitting/receiving unit beforeand after amplification of the radio signal, the additional measurementresult is transmitted via the cable to the transmitting receiving unit.The additionally measured level is transmitted via the cable to thetransmitting/receiving unit, and a further level difference between themeasured levels is determined. If there is any discrepancy in thefurther level difference, this is included in the influence on thetransmitted signal. This measure also allows different gain factors,caused by severe temperature fluctuations, of the antennatransmitting/receiving unit to be detected and to be compensated for byincluding the measurement result in the transmitted signal levelcontrol.

The measurements of the level of the transmitted signal areadvantageously carried out continuously or at regular time intervals.Continuous measurement of the level allows detailed control of the levelwhile, in contrast, the measurement of time intervals means a reduceddynamic load on a microprocessor which is used for the method accordingto the present invention. In the case of measurement at regular timeintervals, there is no need for integration of the measured values, viawhich hectic control action is smoothed out. In the case of continuousmeasurement, the measured level values of the level of the transmittedsignal are advantageously integrated.

The levels are measured as voltage or power levels and the leveldifference is determined as a power level difference, with the levelbeing converted to a power level if the voltage level is measured.

According to a further advantageous embodiment of the method of thepresent invention, the transmitted signal is input, and the receivedsignal which is received with the aid of the antenna is output in thetransmitting/receiving unit with the aid of a diplexer which isconnected to the cable, with the transmitted signal being passed via acontrollable attenuater and an amplifier to the diplexer. Thetransmitted signal is output and the received signal is input in theantenna transmitting/receiving unit with the aid of a diplexer which isconnected to the cable, The transmitted signal is passed via an antennatransmission amplifier and the received radio signal is passed via anantenna reception amplifier. The transmitted signal is input and thereceived signal is output in the antenna transmitting/receiving unitwith the aid of a further diplexer which is connected to the antennacable. The level of the transmitted signal is, in each case, measuredwith the aid of level meters which are arranged in both the antennatransmitting/receiving unit and in the transmitting/receiving unit, anda setting signal is calculated in the transmitting/receiving unit, withthe aid of a microprocessor, in order to set the attenuater. Theadvantageous control of the transmitted signal level with the aid of acontrollable attenuater allows level control to be achieved over a widelevel range.

In an installation of the transmitting/receiving unit configurationexplained above, the level of the transmitted signal is measured, andthe level difference is determined in both the antennatransmitting/receiving unit and the transmitting/receiving unit, and thelevel difference is set with the aid of the attenuater in such a mannerthat a level which is dependent on the transmission method is measuredin the antenna transmitting/receiving unit. This level difference whichis set is kept approximately constant during continuous operation withthe aid of the attenuater. Alternatively, the variable attenuator can beset to a basic setting by the measured level difference between the twotransmitting/receiving units and, in the course of operation, the leveldifference of the transmitted signal is measured before and afteramplification in the antenna transmitting/receiving unit, wherein theattenuater is set as appropriate for the level difference. This assumesthat, once the transmitting/receiving unit configuration has beenstarted up, the transmission characteristics of the cable vary less thanthose of the temperature-dependent antenna transmission amplifier, thatis, considerably greater level fluctuations are caused by the antennatransmission amplifier. In addition, the level difference caused by thecable should be determined at relatively long time intervals, and thevariable attenuater should be set as appropriate for the leveldifference discrepancies which are determined.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Preferred Embodiments and the Drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram schematic of an arrangement forimplementing the method according to the teachings of the presentinvention; and

FIG. 2 shows a flow chart of the steps of the method of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a radio base station BS which is connected via a cable L toan antenna transmitting/receiving unit ASE. The cable L may be formed bywidely different types of coaxial cable with widely differentattenuating fittings. The antenna transmitting/receiving unit ASE isconnected directly to an antenna A, in which case the antennatransmitting/receiving unit ASE and the antenna A can be arranged eithera housing or separately. In addition, further connections are provided;for example, for the power supply and for interchanging informationbetween the transmitting/receiving unit SE and the antennatransmitting/receiving unit ASE.

In the radio base station BS the cable L is passed to atransmitting/receiving unit SE, in which the cable L is connected to afirst diplexer W1. For the exemplary embodiment, it is assumed that aradio-frequency transmitted signal fs, which is intended for radiotransmission is formed in the radio base station BS and is transmitted,to a first, variable attenuater DG1 arranged in thetransmitting/receiving unit SE. The first attenuater DG1 is, forexample, in the form of a controllable Pin diode and is, furthermore,connected to a first amplifier V1 in which the radio-frequencytransmitted signal fs is amplified. The radio-frequency transmittedsignal fs is then input into the cable L with the aid of the firstdiplexer W1. The radio-frequency transmitted signal fs transmitted viathe cable L is output in the antenna transmitting/receiving unit ASEwith the aid of a second diplexer W2 and is passed to an antennatransmission amplifier AV. The transmitted signal fs is amplified to therequired transmission power or to an intended transmission power withthe aid of the antenna transmission amplifier AV, which is also referredto in the specialist field as a high power amplifier HPA. After thisamplification of the radio-frequency transmitted signal fs, this signalis transmitted via a third diplexer W3 to the antenna A and is input tothe connection which leads to the antenna A. The method according to thepresent invention relates essentially to the transmission path asdescribed above.

However, radio signals are also received with the aid of the antenna A,as received signals es, in a radio base station BS and in the antennatransmitting/receiving unit ASE. The received signal es is output withthe aid of the third diplexer W3 and, after amplification by an antennareception amplifier EV, which is also referred to as a low noiseamplifier LNA in the specialist field, is input into the cable L withthe aid of the second diplexer W2. The transmitted received signal es ispassed to a second variable attenuater DG2, with the aid of the firstdiplexer W1, in the transmitting/receiving unit SE. The received signales is then amplified with the aid of a second amplifier V2 in such amanner that it can be transmitted to those components—not illustrated—ofthe radio base station BS which carry out the further processing.

According to the present invention, the level of the radio-frequencytransmitted signal fs passed to it is measured in thetransmitting/receiving unit SE with the aid of a first level measurementdevice PM1. A first sensor S1 is provided for outputting the measurementsignal ms. The output measurement signal is measured in the first levelmeasurement device PM1, is converted to digital information representingthe logarithm of the measured level value pw1, and is transmitted to amicroprocessor MP, which is indicated in FIG. 1 by an arrow denoted pw1.From this microprocessor MP, an additional connection V (for example, inthe form of a two-core copper cable) is passed together with the cable Lto the antenna transmitting/receiving unit ASE where it is connected toa second level measurement device PM2. A second sensor S2, which isarranged upstream of the antenna transmission amplifier AV, and a thirdsensor S3, which is arranged downstream of the antenna transmissionamplifier AV, are connected to this second level measurement device PM2.A measurement signal ms is in each case output with the aid of these twosensors S2, S3, and is transmitted to the second level measurementdevice PM2. These measurement signals are measured analogously to thefirst level measurement device PM2, and information which representsdigital level measured values pw2, pw3 is formed and transmitted via theconnection V to the microprocessor MP, which is indicated in FIG. 1 byan arrow denoted pw2, pw3.

The method according to the present invention will be explained in moredetail with reference to a flowchart which is illustrated in FIG. 2.FIG. 2 shows the sequence of a measurement routine MR which is carriedout in the microprocessor MP. The measurement routine MR is initializedduring the starting up of the radio base station BS, and a predeterminedvalue vw is read in and stored. The reading-in process takes place, forexample, via a data interface DS, which is connected to a control unit(not illustrated) of the radio base station, with the predeterminedvalue vw being either stored in a memory in the control unit ortransmitted to the control unit via an operational interface (notillustrated). The predetermined value vw indicates the level differenceat which the radio-frequency transmitted signal ts which is passed viathe transmitting/receiving unit SE, the cable (L) and the antennatransmitting/receiving unit ASE should be maintained. The measurementroutine MR then forms a first and a second level measurement requestmwa1, mwa2, and transmits this to the first and second level measurementdevices PM1, PM2. A measured value mw which is present at the sensors S1. . . 3 is then detected in the two level measurement devices PM1, PM2,and is transmitted in digital form to the microprocessor MP, asinformation representing first to third level measured values pw1 . . .3.

Various level differences are determined in this microprocessor MP. Thevalue pdw1 of a first level difference is formed by subtracting thefirst and second level measured values pw1, pw2. Furthermore, a valuepdw2 for a second level difference is formed by subtracting the secondand third level measured values pw2, pw3. The value pdw3 of a thirdlevel difference is formed by adding these two values pdw1, pdw2. Thevalue pdw3 of this third level difference represents the overall gainfactor of the radio-frequency transmitted signal fs which is passed viathe transmitting/receiving unit SE, the cable (L) and the antennatransmitting/receiving unit ASE.

When the radio base station BS is started up, the value pdw3 of thethird level difference is compared with the predetermined value vw, andthe discrepancy is determined. This discrepancy represents the one basicsetting information item ei′ which is transmitted to the first andsecond attenuaters DG1, 2. This setting information ei is used, inparticular, to set the attenuation of the first attenuater DG1 such thatthe value pdw3 of the third level difference and the predetermined valuevw are approximately the same. This means that the previously explainedoverall gain factor is approximately equal to the predetermined value.This basic setting information ei′ is used to set the first variableattenuater DG1 to a basic attenuation level. Since this setting isgoverned, in particular, by the cable characteristics, in thecharacteristics of the coaxial cable which is being used, the firstattenuater DG1 is set to a low attenuation for cables L having highlevel attenuations, and is set to a high attenuation for cables L havinga low level attenuation.

During operation of the radio base station BS, the setting informationei can be formed by either of the values pdw2, pdw3 of the third leveldifference. The setting information ei is formed as on startup if it isformed by the value pdw3 of the third level difference. If the settinginformation ei is formed by the value pdw2 of the second leveldifference, the discrepancies between the value pdw2 of the second leveldifference and the value pdw2 determined on startup are determined,wherein this discrepancy governs the setting information ei. Thissetting information ei is used essentially to compensate for differentgain factors in the antenna transmission amplifier AV caused by thesevere temperature fluctuations. If the setting information ei is formedby the value pdw2 of the second level difference, the value pdw1 of thefirst level difference is also checked (not illustrated in FIG. 2) atrelatively lengthy time intervals in order to correct, for example, forany change in the attenuation of the cable L, which is likewise causedby temperature fluctuations.

Different predetermined values can be loaded in the microprocessor MPvia a higher level device, for example a network management device, in aradio communications network (not illustrated) in order to influence aremotely controlled setting of the sizes of radio cells governed by thelevel of the transmitted signal fs. This allows radio cells to beconfigured and, if necessary, position changes of the radio base stationBS to be avoided. In addition, the level of the radio signal at theboundaries of the radio cells can be set so as to ensure that thenetwork termination device is operated without interference.

Furthermore, the level ratios which are determined for the transmissionpath and which are influenced by different cables L and gain factorsalso can be transmitted on the transmission path (not illustrated inFIG. 2). For this purpose, a further setting information item eie isformed, which is used to set the second attenuater DG2. The settinginformation ei, eie for the transmission and reception paths is, in thiscase, approximately the same. As a result, the setting of the secondvariable attenuater DG2 is approximately the same.

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the invention as set forth in the hereafter appended claims.

What is claimed is:
 1. A method for influencing a level of aradio-frequency transmitted signal, the method comprising the steps of:passing the transmitted signal to a transmitting/receiving unit;measuring the level of the transmitted signal in thetransmitting/receiving unit; transmitting the transmitted signal fromthe transmitting/receiving unit via a cable to an antennatransmitting/receiving unit which is connected to an antenna; amplifyingthe transmitted signal in the antenna transmitting/receiving unit andmeasuring the level of the transmitted signal in the antennatransmitting/receiving unit both before and after amplification;determining a first level difference between the level of thetransmitted signal in the transmitting/receiving unit and the level ofthe transmitted signal in the antenna transmitting/receiving unit beforeamplification; determining a second level difference between the levelof the transmitted signal in the antenna transmitting/receiving unitbefore amplification and the level of the transmitted signal in theantenna transmitting/receiving unit after amplification; using the firstand second level differences to determine an overall gain; comparing theoverall gain with a predetermined level difference; and influencing thelevel of the transmitted signal such that the overall gain is maintainedapproximately at the predetermined level difference.
 2. A method forinfluencing the level of a radio-frequency transmitted signal as claimedin claim 1, wherein the steps of comparing and influencing are carriedout in one of the transmitting/receiving unit and the antennatransmitting/receiving unit, such that the measured levels of thetransmitted signal are respectively transferred to thetransmitting/receiving unit and the antenna transmitting/receiving unit.3. A method for influencing the level of a radio-frequency transmittedsignal as claimed in claim 1, wherein the steps of measuring the levelof the transmitted signal are carried out one of continuously and atregular time intervals.
 4. A method for influencing the level of aradio-frequency transmitted signal as claimed in claim 1, wherein themeasured levels of the transmitted signal are integrated.
 5. A methodfor influencing the level of a radio-frequency transmitted signal asclaimed in claim 1, wherein the levels of the transmitted signal aremeasured as one of voltage and power levels, the level difference beingdetermined as a power level difference with the level being converted toa power level if the voltage level is measured.
 6. A method forinfluencing the level of a radio-frequency transmitted signal as claimedin claim 1, wherein the transmitted signal is formed using a CDMA accessmethod.
 7. A method for influencing the level of a radio-frequencytransmitted signal as claimed in claim 1, the method further comprisingthe steps of: inputting the transmitted signal in thetransmitting/receiving unit, the transmitted signal being passed via acontrollable attenuator and an amplifier to a first diplexer; outputtinga received signal, which is received with the aid of the antenna, in thetransmitting/receiving unit with the aid of the first diplexer which isconnected to the cable; outputting the transmitted signal in the antennatransmitting/receiving unit, the transmitted signal being passed via anantenna transmission amplifier; inputting the received signal in theantenna transmitting/receiving unit with the aid of a second diplexerwhich is connected to the cable, the received signal being passed via anantenna reception amplifier; inputting the transmitted signal in theantenna transmitting/receiving unit; outputting the received signal inthe antenna transmitting/receiving unit with the aid of a third diplexerwhich is connected to the antenna; measuring the level of thetransmitted signal in both the transmitting/receiving unit and theantenna transmitting/receiving unit with the aid of first and secondlevel meters, respectively; and calculating a setting signal in thetransmitting/receiving unit with the aid of a microprocessor so as toset the attenuator, the setting signal representing the discrepanciesbetween the determined and the predetermined level difference.
 8. Amethod for influencing the level of a radio-frequency transmitted signalas claimed in claim 1, the method further comprising the step of:influencing the level of the received signal by a further attenuator,the received signal being passed via a further amplifier in thetransmitting/receiving unit.
 9. A method for influencing the level of aradio-frequency transmitted signal as claimed in claim 1, wherein thetransmitted signal is formed by a radio-frequency signal which isintended for transmission via a radio path.
 10. A method for influencingthe level of a radio-frequency transmitted signal as claimed in claim 1,wherein the levels of the transmitted signal which are measured in thetransmitting/receiving unit and the antenna transmitting/receiving unitare respectively transmitted via at least one separate connection to thetransmitting/receiving unit and the antenna transmitting/receiving unit.